Appropriate nutrition requires that all nutrients, carbohydrates, lipids, proteins, minerals, vitamins and water are ingested in adequate amounts and in the correct proportions. This is essential for normal organ development and function, reproduction, repair of body tissues and combating stress and disease. The nutrient intake must also be adjusted for varied levels of activity and physical work. Beyond those basic elements, however, it has been found that diet, particularly protein intake, has a profound effect on learning, behavior and mood.
It has been shown in humans and other species that certain amino acids directly influence brain activity and behavior by enhancing or reducing the rate of synthesis of various neurotransmitters. Noradrenaline induces high states of arousal and has been implicated in the generation of aggressive behavior. Dopamine is involved in motor coordination, attention, reinforcement and reaction time. Serotonin plays a role in the regulation of mood, the control of sleep and arousal, the regulation of pain and in the control of eating. Low serotonin levels have been demonstrated in individuals showing impulsivity, aggressive behavior, anti-social behavior, attention deficit/hyperactivity disorder, agitation, anxiety and learning problems. A lack of serotonin may cause a reduction in the ability to learn new or alternative behaviors.
Ingested protein is broken down into its component amino acids. It is well known that the amino acids tryptophan and tyrosine are converted to neurotransmitters in the mammalian brain. Tyrosine is converted to the catecholamine stimulants adrenaline, dopamine and noradrenaline, while tryptophan is converted to serotonin. The balance between the two families of neurotransmitters defines the mood of the mammal. A tip in the balance toward catecholamine is manifested in certain forms of aggression and hyperactivity, while high serotonin levels tend to induce calmness.
Most of the studies have been done in humans, although corollaries can be noted to other species. The canine corollaries to human findings may exhibit as aggression, anxiety, over activity/excitability, the inability to learn new behaviors and general touch sensitivity. In other words, the balance has been tipped to the catecholamines.
Humans and dogs experiencing emotional disorders have been treated to raise serotonin levels by tryptophan supplementation or by administration of serotonin reuptake inhibitors, which increase the dwell time on neural synapses, thus increasing the serotonin effect. U.S. Pat. No. 5,762,960, issued Jun. 9, 1998, discloses the use of several known serotonin reuptake inhibitors to reduce aggression in dogs. Conversely, Wurtman in U.S. Pat. No. 4,435,424, issued May 6, 1984, suggests the benefits of adding tyrosine to the diet of humans in order to raise catecholamines in low-energy subjects. This use of administered drugs to change the balance of catecholamines to serotonin is well known in both medical and veterinary practice.
Whatever the treatment, the patient must ingest a good balanced diet, a diet that provides sufficient energy as well as sources of monoamines for brain function. It is well known that the brain is very sensitive to any change in the level of sugar in the blood, and therefore this is usually under very careful control. However, if there is a fault in the mechanism controlling the levels of blood sugar, which then fall to a hypoglycemic state, the function of the brain becomes impaired and certain physical and behavioral changes take place. Following a meal, the level of sugar in the blood rises, in response to which, insulin is secreted and glucose diverted to the liver where it is stored as glycogen. The process is reversed when blood sugar levels are low. The liver continually secretes glucose back into the blood to convert to energy which is vital to life functions. The amount of glycogen stored in the liver is insufficient to maintain normal blood sugar levels for more than a short time. During periods of deprivation of blood glucose, the tissues gain their energy from various non-carbohydrate source but this deprives the brain of amino acids to be converted to neurotransmitters.
Dogs can thrive on a large number of very different food materials. Although classed in the order Carnivora, dogs are not strict carnivores, but like humans, are omnivorous and able to utilize nutrients from plant sources as well as animal sources. Carnivores are generally considered to be once-a-day, or less often feeders, gorging when food is available and fasting in between feasts. This is suitable for life in the wild. Many domestic pets are fed once a day, mimicking the case of the wild carnivore. The large daily meal is followed by a period of torpor and then by a period of increased activity. These mood swings are not compatible with indoor life as a pet and are considered to result in behavior problems.
Some dogs may not be able to tolerate periods of fasting, due to impaired liver function or inadequate diet to provide energy requirements. Each dog's dietary and exercise requirements are different and their ability to utilize constituents of their diet will vary. These factors have a direct influence on behavior. For example, low blood sugar can result in a reduced level of response, shallow breathing, muscle tremors and a change from normal behavior to confusion, agitation and aggression.
In assessing behavior problems, low blood sugar levels could give an indication of the underlying cause when no other has been identified. Low blood sugar levels may be partly responsible for the frequently observed aggressive state in dogs awakening abruptly from deep sleep, a time at which the brain has insufficient energy to make rational decisions, which the primitive basic survival instincts of fight/flight are active.
Dog owners need a simple dietary regimen to stabilize and improve the learning capability, mood and behavior of their dogs without reliance on pharmacological intervention. Similarly, felines, horses and humans can benefit from such simple regimens, which can easily be integrated into daily care. It is desirable to find a way to mimic a dietary regimen by supplementation of the diet.